Due to increased levels of toxicity caused by chemicals found within the water supply, water filtration has become widespread within many homes. Point-of-use (POU) water treatment devices are designed to treat small amounts of drinking water for use in the home. These devices can sit on the counter, attach to the faucet, or be installed under the sink. They differ from point-of-entry (POE) devices, which are installed on the water line as it enters the home and treats all the water in the building.
Many households today have Reverse-Osmosis (RO) units installed. Reverse-osmosis devices are usually installed underneath the sink, with the tap water connection plumbed directly to the sink cold water supply line, and a waste water drain line connected directly to the sink p-trap. These devices use a membrane that screens out chemicals, such as chloride and sulfate as well as most other contaminates found in the water supply today. A RO system can remove particles down to 1 Angstrom. However POU RO systems can waste as much as 3 to 4 gallons of water for every gallon that is treated. This is due to a continuous flow of water that is required across the membrane surface to remove contamination and to keep the membrane from clogging up.